The present invention relates to a method for extracting a gaseous fluid. More particularly, it concerns with a method for extracting a gaseous fluid which is capable of suppressing the entrainment of fine particles and mist, curtailing clogging of a filter and the like, and ensuring a stable operation in the case of extracting a gaseous fluid through an extraction port set up on the top face portion of a vertical-type agitation tank.
In the case of extracting a gaseous fluid through an extraction port placed on the top face portion of a vertical-type agitation tank, there is generally taken a countermeasure for preventing the entrainment of the content of the tank, for instance, the entrainment of solids in an agitation tank the content of which is in the form of solid, and the entrainment of mist in an agitation tank the content of which is in the form of liquid. Specifically, in these cases there is generally taken a countermeasure of assuring a space from the surface of the content to the top face portion of the agitation tank, spraying a liquid at a high velocity, or setting up a baffle plate in the vicinity of a fluid extraction port inside the agitation tank.
However, in the case of scaleup of the treatment capacity of the above-mentioned vertical-type agitation tank, when being geometrically similar, the tip velocity of an agitation blade increases with an increase in a superficial velocity of the gaseous fluid in the tank, whereby the swirling velocity increases and thus, the entrainment of fine particles and mist (hereinafter sometimes referred to as xe2x80x9cEntraixe2x80x9d) is directed to acceleration.
Since the spraying effect is decreased in the case of the agitation tank being in a high pressure system, the above-mentioned problem of entrainment becomes further conspicuous, thus unreasonably increasing the frequency of replacing a filter set up on the downstream side of the fluid extraction port. As a result, continuous operation of the agitation tank is made impossible thereby as the case may be. As mentioned hereinbefore, in the case of scaleup of the treatment capacity of the agitation tank, an effective suppressing method for the xe2x80x9cEntraixe2x80x9d is made indispensable.
It is a general procedure in a vertical-type agitation tank to locate a gaseous fluid extraction port at the center of the top face portion thereof. In this case, even if there exists no problem of entrainment in particular in a small scale of an agitation tank, a large scale thereof sometimes exaggerates the aforesaid problem to the extent that an ordinary operation is disturbed by an increased amount of entrainment due to the synergistic effect of swirling flow and upward flow.
In the case of a vertical-type agitation reaction tank equipped with one gaseous fluid extraction port at a position eccentric from the center of the top face portion thereof, there is raised a problem in that internal swirling flow is made nonuniform by the influence of the aforesaid extraction port, and thus liquid propylene as a coolant which is sprayed for cooling is not uniformly distributed on the surface of powders, thereby inducing un-even temperature distribution inside the reaction tank.
In FIG. 1 and FIG. 2, (a) a schematic side view and (b) a schematic plan view, respectively shows the positions of fluid extraction ports set up on the top face portion of a conventional vertical-type agitation tank whose positions are different from each other. The vertical-type agitation tank illustrated on FIG. 1 contains a content 5 and has such a structure that is equipped with an agitator 2 inside an approximately cylindrical tank 1 and with one fluid extraction port 4 approximately at the center A of the top face portion 3 (the same also applies to the followings).
The vertical-type agitation tank illustrated on FIG. 2 has such a structure that is equipped with an agitator 2 inside an approximately cylindrical tank 1 and with one fluid extraction port 4 at a position eccentric from the center A of the top face portion 3.
On the other hand, there is disclosed a vertical-type agitation reaction tank equipped with two fluid extraction ports at two positions of the top face portion in Japanese Patent Publication No. 30539/1977 (Shouwa 52). The above-mentioned two fluid extraction ports in the reaction tank are each set up at a position eccentric from the center of the top face portion, and not at a symmetrical position about the center. However, problems such that the working effect on suppressing the entrainment is limited, a spraying liquid for cooling is not uniformly distributed on the surface of the content are raised, thus it is likely to bring about unstable reaction due to non-uniform cooling as well as xe2x80x9cEntraixe2x80x9d.
In such circumstances, an object of the present invention is to provide a method for extracting a gaseous fluid which is capable of suppressing the entrainment of fine particles and mist, curtailing clogging of a filter and the like, contriving uniformization for the temperature of the content and at the same time, ensuring a stable operation in the case of extracting a gaseous fluid through extraction ports set up on the top face portion of a vertical-type agitation tank.
As the result of intensive extensive research and investigation accumulated by the present inventors, it has been found that the above-mentioned object is achieved by setting up two extraction ports at positions that are approximately symmetrical about the center of the upper side portion of a vertical-type agitation tank, or at least three extraction ports each at a vertex of an approximately regular polygon (at least an equilateral triangle) having the central point identical with the center of the top face portion of the vertical-type agitation tank, or one extraction port approximately at the center of the top face portion thereof in addition to the above-mentioned two or at least three extraction ports, since the internal swirling flow is uniformized, the influence of the swirling flow in the vicinity of the extraction ports can be minimized, whereby the amount of the entrainment can be curtailed and at the same time, a liquid to be sprayed for the purpose of cooling and suppressing the entrainment can be uniformly distributed. Such being the case, the present invention has been accomplished on the basis of the foregoing findings and information.
Specifically, the present invention provides (1) a method for extracting a gaseous fluid which comprises extracting a gaseous fluid through extraction ports set up on the top face portion of a vertical-type agitation tank equipped inside with an agitator, characterized in that two extraction ports are set up at positions approximately symmetrical about the center of the top face portion of said vertical-type agitation tank or as the case may be, additional one extraction port is set up approximately at the center of the top face portion thereof; and (2) a method for extracting a gaseous fluid which comprises extracting a gaseous fluid through extraction ports set up on the top face portion of a vertical-type agitation tank equipped inside with an agitator, characterized in that at least three extraction ports are installed each at a vertex of an approximately regular polygon (at least an equilateral triangle) having the central point identical with the center of the top face portion of the vertical-type agitation tank or as the case may be, additional one extraction port is set up approximately at the center of the top face portion thereof.
In addition, a preferred embodiment according to the present invention comprises a method in which the above-mentioned vertical-type agitation tank is equipped with a spraying mechanism in the vicinity of any of the internal fluid extraction ports.